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Eric, Technician
Category: Motorcycle
Satisfied Customers: 1533
Experience:  MMI grad. 7 years experience in Honda, Suzuki, Yamaha, as service manager and tech.
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1980 Honda: temperature gauge..the voltage..12V..engine starts

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I recently bought a 1980 Honda CX500. The temperature gauge did not work and the mechanic at the Honda shop told me there was a gizmo that reduces the voltage to the gauge from 12V to 9V, and it is no longer available. He bypassed the defective unit and the gauge pegs out as soon as the engine starts to warm up.

I hesitate to run the bike too far from home without a functioning gauge. This is the only thing wrong with it, otherwise it's really a nice bike. What would you suggest?


was any other parts replaced or tested? like possibly the thermo sensor? i dont see that diagnosis correct.

Customer: replied 5 years ago.

I'm not at all sure what the mechanic did except for what he told me. The gauge worked when I bought the bike, but quit shortly thereafter. I took it to the shop and the mechanic said it could not be fixed because the voltage reducer thing was no longer manufactured. I suspect he didn't evaluate the thermo sensor, he said he did something with the wiring to get a reading on the heat gauge even though it was not accurate. I guess he would have done more, but I decided to pay him for the diagnostics he did already, and take it from there myself.


Would it be possible to install an aftermarket heat gauge?

the reason i say this may not be correct info is because the temp gets its reading from a sensor. that sensor is located on the thermostat housing. that is toward the rear of the motor, i believe toward the under side of the carbs on the left. you should see a sensor with a single wire coming from. the sensor is screwed into the thermostat housing. this sensor is still available. it would be good information to know what exactly the mechanic did to correct this. because if all you needed was that sensor. or make sure the wire to that sensor was fine, that it isnt spliced elsewhere. because say you got a new sensor and plugged it in, if he altered the wiring, then you wouldn't know if it works for sure or not. however to answer your question there is an aftermarket gauge you can get. it plugs inline with a coolant hose. here is a link to the part.

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